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United States Patent |
6,042,463
|
Johnson
,   et al.
|
March 28, 2000
|
Polycrystalline diamond compact cutter with reduced failure during
brazing
Abstract
A supported polycrystalline compact (PC) cutter made under high
temperature, high pressure (HT/HP) processing conditions having non-planar
interfaces between the PC layer and a cemented carbide support layer. The
carbide PC interface geometry is such that one or more protrusions extend
from the support layer into the PC layer. The protrusions have a low
cobalt metal binder content of about 3-9% by weight. The low cobalt metal
binder content in the protrusions results in enhanced performance and
improved resistance to cracking during installation and/or to brazing
breakage.
Inventors:
|
Johnson; David M. (Westerville, OH);
Klug; Frederic J. (Schenectady, NY)
|
Assignee:
|
General Electric Company (Pittsfield, MA)
|
Appl. No.:
|
975028 |
Filed:
|
November 20, 1997 |
Current U.S. Class: |
451/540; 51/309; 451/548 |
Intern'l Class: |
B23F 021/03 |
Field of Search: |
125/3,28
451/540,548
51/307,309
|
References Cited
U.S. Patent Documents
2978847 | Apr., 1961 | Shoemakers | 451/548.
|
3141746 | Jul., 1964 | DeLai.
| |
3256646 | Jun., 1966 | Mockli | 451/548.
|
3609818 | Oct., 1971 | Wentorf, Jr.
| |
3745623 | Jul., 1973 | Wentorf, Jr. et al.
| |
3850591 | Nov., 1974 | Wentorf, Jr.
| |
4394170 | Jul., 1983 | Sawaoka et al.
| |
4403015 | Sep., 1983 | Nakai et al.
| |
4784023 | Nov., 1988 | Dennis.
| |
4794326 | Dec., 1988 | Friedl.
| |
4954139 | Sep., 1990 | Cerutti.
| |
4972637 | Nov., 1990 | Dyer.
| |
5007207 | Apr., 1991 | Phaal | 451/548.
|
5199832 | Apr., 1993 | Meskin et al. | 451/548.
|
5467669 | Nov., 1995 | Stroud.
| |
5484330 | Jan., 1996 | Flood et al.
| |
5486137 | Jan., 1996 | Flood et al.
| |
5494477 | Feb., 1996 | Flood et al.
| |
5885149 | Mar., 1999 | Gillet et al. | 451/548.
|
Foreign Patent Documents |
0 604 211 A1 | Jun., 1994 | EP.
| |
0 706 981 A2 | Apr., 1996 | EP.
| |
0 699 817 A2 | Sep., 1996 | EP.
| |
Primary Examiner: Eley; Timothy V.
Claims
What is claimed is:
1. An improved abrasive tool insert comprising:
an abrasive layer; and
a cemented carbide substrate having a metal binder therein and is bonded to
said abrasive layer;
wherein one or more cemented carbide protrusions extend from said substrate
into said abrasive layer, and wherein the metal binder content in each of
said protrusions is less than the metal binder content of said substrate.
2. A tool insert according to claim 1 wherein said abrasive layer is
composed of polycrystalline diamond.
3. A tool insert according to claim 1 wherein said cemented carbide is
tungsten carbide.
4. A tool insert according to claim 1 wherein said metal binder is selected
from the group consisting of cobalt, iron, nickel, platinum, titanium,
chromium, tantalum and alloys thereof.
5. A tool insert according to claim 1 wherein the metal binder content in
said protrusions ranges from about 3-9% by weight on average and the metal
binder content of said substrate ranges from about 10-16% by weight on
average.
6. A tool insert according to claim 1 wherein said protrusions are pyramid,
cone or truncated-cone shaped.
7. A tool insert according to claim 1 wherein said protrusions are block
shaped.
8. A tool insert according to claim 1 wherein said protrusions are
sinusoid, ellipsoid or sphere shaped.
9. An improved abrasive tool insert comprising:
a polycrystalline diamond layer; and
a tungsten carbide substrate bonded to said diamond layer;
said tungsten carbide substrate has a metal binder content of from about
10-16% by weight on average; and
wherein one or more tungsten carbide protrusions extend from said tungsten
carbide substrate into said diamond layer, said tungsten carbide
protrusions having a binder metal content ranging from about 3-9% by
weight on average.
10. An improved abrasive tool insert according to claim 9 wherein said
protrusions are pyramid, cone or truncated-cone shaped.
11. An improved abrasive tool insert according to claim 9 wherein said
protrusions are block shaped.
12. An improved abrasive tool insert according to claim 9 wherein said
protrusions are sinusoid, ellipsoid or sphere shaped.
Description
FIELD OF THE INVENTION
The present invention relates to supported polycrystalline diamond compacts
(PDCs) made under high temperature, high pressure (HT/HP) processing
conditions, and more particularly to supported PDC compacts having
non-planar interfaces between the PDC layer and the cemented carbide
support layer. The object of the present invention is to provide a PDC
cutter with improved resistance to cracking during installation.
BACKGROUND OF THE INVENTION
Abrasive compacts are used extensively in cutting, milling, grinding,
drilling and other abrasive operations. The abrasive compacts typically
consist of polycrystalline diamond or cubic boron nitride particles bonded
into a coherent hard conglomerate. The abrasive particle content of
abrasive compacts is high and there is an extensive amount of direct
particle-to-particle bonding. Abrasive compacts are made under elevated
temperature and pressure conditions at which the abrasive particle, be it
polycrystalline diamond or cubic boron nitride, is crystallographically
stable.
Abrasive compacts tend to be brittle and, in use, they are frequently
supported by being bonded to a cemented carbide substrate. Such supported
abrasive compacts are known in the art as composite abrasive compacts. The
composite abrasive compact may be used as such in the working surface of
an abrasive tool. Alternatively, particularly in drilling and mining
operations, it has been found advantageous to bond the composite abrasive
compact to an elongated cemented carbide pin to produce what is known as a
stud cutter. The stud cutter is then mounted in the working surface of a
drill bit or a mining pick.
Fabrication of the composite is typically achieved by placing a cemented
carbide substrate into the container of a press. A mixture of diamond
grains or diamond grains and catalyst binder is placed atop the substrate
and compressed under HT/HP conditions. In so doing, metal binder migrates
from the substrate and "sweeps" through the diamond grains to promote a
sintering of the diamond grains. As a result, the diamond grains become
bonded to each other to form a diamond layer, and that diamond layer is
bonded to the substrate along a conventionally planar interface. The metal
binder occupies the space between the diamond grains with little or no
porosity in the sintered compact. Methods for making diamond compacts and
composite compacts are more fully described in U.S.Pat. Nos. 3,141,746
('746); 3,745,623('623); 3,609,818 ('818); 3,850,591 ('591); 4,394,170
('170); 4,403,015 ('015); 4,794,326 ('326); and 4,954,139 ('139), the
disclosures of which are expressly incorporated herein by reference.
A composite formed in the above-described manner may be subject to a number
of shortcomings. For example, the coefficients of thermal expansion and
elastic constants of cemented carbide and diamond are different. Thus,
during heating or cooling of the PDC, thermally induced stresses occur at
the interface between the diamond layer and the cemented carbide
substrate. The magnitude of these stresses is dependent on the applied
pressure, the temperature of zero stress and the disparity in thermal
expansion coefficients and elastic constants.
Another potential shortcoming which should be considered relates to the
creation of internal stresses within the diamond layer which can result in
a fracturing of that layer. Such stresses also result from the presence of
the cemented carbide substrate and are distributed according to the size,
geometry and physical properties of the cemented carbide substrate and the
polycrystalline diamond layer.
European Patent Application No. 0133 386 suggests PDC in which the
polycrystalline diamond body is completely free of metal binders and is to
be mounted directly on a metal support. However, the mounting of a diamond
body directly on metal presents significant problems relating to the
inability of the metal to provide sufficient support for the diamond body.
The European Patent Application further suggests the use of spaced ribs on
the bottom surface of the diamond layer which are to be embedded in the
metal support.
According to the European Patent Application, the irregularities can be
formed in the diamond body after the diamond body has been formed, e.g.,
by laser or electronic discharge treatment, or during the formation of the
diamond body in a press, e.g., by the use of a mold having irregularities.
As regards the latter, it is further suggested that a suitable mold could
be formed of cemented carbide; in such case, however, metal binder would
migrate from the mold and into the diamond body, contrary to the stated
goal of providing a metal free diamond layer. The reference proposes to
mitigate this problem by immersing the thus-formed diamond/carbide
composite in an acid bath which would dissolve the carbide mold and leach
all metal binder from the diamond body. There would thus result a diamond
body containing no metal binder and which would be mounted directly on a
metal support. Notwithstanding any advantages which may result from such a
structure, significant disadvantages still remain, as explained below.
In sum, the European Patent Application proposes to eliminate the problems
associated with the presence of a cemented carbide substrate and the
presence of metal binder in the diamond layer by completely eliminating
the cemented carbide substrate and the metal binder. However, even though
the absence of metal binder renders the diamond layer more thermally
stable, it also renders the diamond layer less impact resistant. That is,
the diamond layer is more likely to be chipped by hard impacts, a
characteristic which presents serious problems during the drilling of hard
substances such as rock.
It will also be appreciated that the direct mounting of a diamond body on a
metal support will not, in itself, alleviate the previously noted problem
involving the creation of stresses at the interface between the diamond
and metal, which problem results from the very large disparity in the
coefficients of thermal expansion between diamond and metal. For example,
the thermal expansion coefficient of diamond is about 45.times.10.sup.7
cm/cm/.degree. C. as compared to a coefficient of 150-200.times.10.sup.7
cm/cm/.degree. C. for steel. Thus, very substantial thermally induced
stresses occur in the cutter.
Recently, various PDC structures have been proposed in which the
diamond/carbide interface contains a number of ridges, grooves or other
indentations aimed at reducing the susceptibility of the diamond/carbide
interface to mechanical and thermal stresses. In U.S. Pat. No. 4,784,023
('023), a PDC includes an interface having a number of alternating grooves
and ridges, the top and bottom of which are substantially parallel with
the compact surface and the sides of which are substantially perpendicular
the compact surface.
U.S. Pat. No. 4,972,637 ('637) provides a PDC having an interface
containing discrete, spaced recesses extending into the cemented carbide
layer, the recesses containing abrasive material (e.g., diamond) and being
arranged in a series of rows, each recess being staggered relative to its
nearest neighbor in an adjacent row. It is asserted in the '637 patent
that as wear reaches the diamond/carbide interface, the recesses, filled
with diamond, wear less rapidly than the cemented carbide and act, in
effect, as cutting ridges or projections. When the PDC is mounted on a
stud cutter, as shown in FIG. 5 of the '637 patent, the wear plane 38
exposes carbide regions 42 which wear much more rapidly than the diamond
material in the recesses 18. As a consequence, depressions develop in
these regions between the diamond filled recesses. The '637 patent asserts
that these depressed regions, which expose additional edges of diamond
material, enhance the cutting action of the PDC cutter.
U.S. Pat. No. 5,007,207 ('207) presents an alternative PDC structure having
a number of recesses in the carbide layer, each filled with diamond, which
make up a spiral or concentric circular pattern, looking down at the disc
shaped compact. Thus, the structure in the '207 patent differs from the
structure in the '637 patent in that, rather than employing a large number
of discrete recesses, the structure of the '207 patent uses one or a few
elongated recesses which make up a spiral or concentric circular pattern.
FIG. 5 in the '207 patent shows the wear plane which develops when the PDC
is mounted and used on a stud cutter. As with the '637 patent, the wear
process creates depressions in the carbide material between the diamond
filled recesses. Like the '207 patent, the '637 patent also asserts that
these depressions which develop during the wear process enhance cutting
action. In addition to enhancing cutting action, non-planer interfaces
have also been presented in U.S. Pat. Nos. 5,484,330 ('330), 5,494,477
('477) and 5,486,137 ('137) which reduce the susceptibility to cutter
failure by have having favorable residual stresses in critical areas
during cutting.
Whereas the aforementioned patents assert a desirable cutting action in the
rock and also favorable residual stresses in during cutting, it is also
highly desirable to minimize the diamond layer's susceptibility to
fracture during installation into the drill bit.
SUMMARY OF THE INVENTION
The present invention relates to supported polycrystalline diamond compacts
made under HT/HP processing conditions, and more particularly to supported
PDCs having improved shear strength and impact resistance properties.
In PDCs, the interface between the tungsten carbide (WC) and the
polycrystalline diamond (PCD) can have a wide variety of surface
geometries. It has been found that WC protrusions (See FIG. 1) into the
PCD layer can often cause cracking of the PCD layer during the brazing of
the cutter onto the bit. This cracking is caused by the thermal mismatch
of the WC and the PCD. By providing WC protrusions with a low Cobalt (Co)
content, cracking of the PDC can be avoided or greatly mitigated during
brazing.
A protrusion is defined as a volume of carbide that protrudes into the PCD
layer and is surrounded on its top and sides by PCD. Examples of this
would be local regions of WC that exist as bumps, dimples, blocks,
saw-tooth shapes, sinusoid shapes, etc., that protrude into the PCD layer.
Another example is grooves in the PCD layer (at the WC-PCD interface)
filled with WC which run completely across the cutter. Many surface
interface geometries are preferred between the WC substrate and the PCD
abrasive layer on a cutter design.
Cracking of the abrasive layer may occur due to: (1) in-process stresses,
(2) residual stresses, (3) thermal stresses which occur during the heating
of the cutter installation (brazing). (Cutters are made using a HT/HP
process.) The subject of this disclosure is to address cracking due to (2)
and (3).
Most PDC cutters are manufactured with a one piece WC support which is
fitted into a refractory metal container which contains the abrasive
un-sintered diamond feed. The object of this invention is to provide a PCD
cutter with improved resistance to cracking during installation by
decreasing the Co level in the WC protrusion into the PCD layer.
Other objects, features, and characteristics of the present invention, as
well as the methods of operation and functions of the related elements of
the structure, will become more apparent upon consideration of the
following detailed description with reference to the accompanying
drawings, all of which form a part of this specification.
BRIEF DESCRIPTION OF THE DRAWINGS
The detailed description below describes the preferred embodiments of the
invention and is intended to be read in conjunction with the following set
of drawings.
FIG. 1 is a cross-sectional view of a PDC cutter showing WC protrusions
with lower Co content than the WC substrate.
FIG. 2a shows finite element model results at 700 C. where the WC
protrusions have normal Co content.
FIG. 2b shows finite element model results at 700 C. where the WC
protrusions have low Co content.
FIG. 3a shows a process for making a PDC cutter in accordance with the
present invention using a grooved WC disc with a low Co content to form
the WC protrusions.
FIG. 3b shows a process for making a PDC cutter in accordance with the
present invention using WC balls with low Co content to form the WC
protrusions.
FIG. 3c shows a process for making a PDC cutter in accordance with the
present invention using WC bars with low Co content to form the WC
protrusions.
FIG. 4a is a low magnification Scanning Electron Microscope (SEM)
photomicrograph that shows interpenetrating protrusions of WC and PCD,
wherein the PCD is the dark material at the top of the photomicrograph.
FIG. 4b is a high magnification SEM photo-micrograph of a portion of FIG.
4a, taken from the corner of one of the WC protrusions, which shows the WC
with depleted Co content.
FIG. 4c is a high magnification SEM photo-micrograph of portion of FIG. 4a,
taken in the center of the WC protrusion, which shows the WC with greater
Co content than at the edge of the protrusion as shown in FIG. 4b.
FIG. 4d is a high magnification SEM photo-micrograph of portion of FIG. 4a,
taken in the center of the WC substrate, which shows the WC with greater
Co content than in the protrusions as shown in FIG. 4b and 4c.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Polycrystalline diamond compacts (PDCs) consist of a polycrystalline
diamond layer (PCD layer) bonded to a carbide substrate. The bond between
the PCD layer and the carbide support is formed at high temperature, high
pressure (HT/HP) conditions. Subsequent reduction of the pressure and
temperature to ambient conditions results in stress development in both
the PCD layer and carbide support due to differences in the thermal
expansion and the compressibility properties of the bonded layers. The
differential thermal expansion and differential compressibility have
opposite effects of stress development as the temperature and pressure are
reduced; the differential thermal expansion tending to cause compression
in the PCD layer and tension in the carbide support on temperature
reduction whereas the differential compressibility tends to cause tension
in the PCD layer and compression in the carbide support.
Finite element analysis (FEA) of stress development and strain gage
measurements confirm that the differential thermal expansion effect
dominates resulting in generally compressive residual stresses (Note:
there are localized zones of tension stresses present) in the PCD layer.
Upon heating a cutter, the diamond stress state will change from being in
general compression to general tension. This "flip" in residual stresses
occur below 700.degree. C. range. The "flip" temperature increases with
decreased bonding pressure (i.e. the pressure where the cutter temperature
reaches the Co freezing point and bonding occurs).
Above the WC protrusions into the PCD layer there are high compressive
stresses in the adjacent PCD layer at room temperature and pressure
conditions. These stresses flip to tensions when the PDC cutter is heated
in a brazing cycle and they can be mitigated in two ways:
(1) increase the "flip" temperature by decreasing the pressure at which the
freezing occurs; or
(2) reduce the Co content in the local region of the protrusion such that
the protrusion's thermal expansion is closer to that of the PCD layer.
This second method is the subject of the present invention. Shown in FIG. 1
is a cross-sectional view of a PDC cutter comprising WC substrate 14 of
normal Co content and WC protrusions 12 into the PCD layer 10 with low Co
content. In this invention it is preferred that protrusions 12 have a Co
content of 6% plus or minus 3%. This will be considered low Co content WC.
The major WC substrate material 14 will have Co content of 13% plus or
minus 3%. This will be considered normal Co content WC. The normal Co
content WC substrate 14 is desirable for impact resistance and tension
strength. The lower Co content WC is desirable only in the zone of
protrusions 12.
FIG. 2a and 2b show finite element model results supporting that method (2)
above does mitigate stresses at brazing temperatures. In FIG. 2a, WC
protrusions 22 comprised normal Co content, and, in FIG. 2b, WC
protrusions 22 comprised low Co content. As indicated in each figure, the
finite element model results show that, at a brazing temperature of
700.degree. C., maximum stress 20 was reduced by 26% through the reduction
of the Co content in WC protrusions 22.
A number of methods for achieving the desired result of low Co content WC
protrusions would be immediately apparent to those of skill in the art.
Some of these are described below.
One method involves placing separate pieces of WC into the HT/HP process
and assembling into the desired geometry. The WC protrusions into the PCD
layer comprise low Co content WC while the rest of the substrate comprises
normal Co content WC. FIGS. 3a, 3b and 3c show some embodiments of this
concept.
Each figure shows the separate pieces to be combined for use in the HT/HP
process and assembled into the desired geometry. A preferred embodiment of
the present invention comprises PCD feed 32, WC substrate 34 with normal
Co content, and any one of the following: 1) WC grooved disc 36 with low
Co content, 2) WC balls 38 with low Co content or 3) WC bars 40 with low
Co content, combined in refractory metal cup 30 as demonstrated in FIG.
3a, 3b and 3c, respectively. These figures represent only a few of the
embodiments of the present invention.
Another method involves having a WC manufacturer supply a graduated Co
content WC substrate in which the WC manufacturer provides integral WC
substrates which have low Co content protrusions and the rest essentially
normal Co content. It is important that it be noted that the decreased Co
content is only desired in the protrusions.
Yet another method, and the most preferred method of the present invention,
consists of controlling the removal of Co from the WC protrusions during
sintering of the PDC cutter. During sintering of the PDC cutter, Co
contained in the WC melts and sweeps into the PCD layer. Preferential
removal of Co from the WC protrusion during sweep of Co from the WC
substrate into the PCD layer would result in a WC protrusion with a lower
thermal expansion, the object of the present invention. The amount of
preferential Co removal can be controlled by altering the geometry of the
WC protrusions and the volume fraction ratio of WC protrusions (into the
PCD layer) to PCD protrusions (into the WC substrate).
FIGS. 4a-d are low (4a) and high (4b,c & d) magnification Scanning Electron
Microscope (SEM) photomicrographs that demonstrate the removal of Co from
the region of the WC substrate adjacent to the PCD layer, with the removal
being dependant on the geometry of the protrusions. FIG. 4a is a low
magnification SEM photomicrograph that shows penetrating protrusions 66 of
WC 60 into PCD layer 50, with PCD layer 50 being the dark material at the
top of the photomicrograph and WC substrate 60 being the light material at
the bottom. FIG. 4a shows the WC-PCD interface 52 at a low magnification
and serves as a reference to the specific source locations of FIGS. 4b, c
and d. The positions of the magnified areas shown in FIG. 4b, c and d are
indicated on FIG. 4a by three squares 70, 80 and 90, respectively, drawn
on the SEM photograph in FIG. 4a.
In FIGS. 4b, c and d, high magnification SEM photomicrographs of specific
portions of FIG. 4a are shown. FIG. 4b, taken from the corner of one of
the WC protrusions 66, shows depleted Co 64 in WC substrate 60 as compared
to the Co content in FIG. 4c which was taken from the center of the
protrusion 66. FIG. 4c, taken from the center of one of the protrusions
66, shows depleted Co 64 in WC substrate 60 as compared to the Co content
in FIG. 4d which was taken in the center of WC substrate 60 a distance
from WC-diamond interface 52.
The depleted Co 64 in the protrusion 66, as shown in FIG. 4b and c, will
result in a desirably lower average thermal expansion for the WC
protrusion 66. These SEM micrographs clearly show that if the surface area
of WC protrusion 66 is high compared to the volume of WC protrusion 66,
then a lower average content of Co 64 and a lower average thermal
expansion coefficient for the protrusion 66 will result. As depicted by
the SEM photomicrographs, FIGS. 4b, c and d, it is clear that the Co
content of the WC substrate is depleted more in the areas closer to the
WC-PCD interface 52.
Therefore, the specific geometry of the WC protrusions 66 effect the
"sweep" of the Co 64 in the WC substrate into the PCD layer 50. The higher
the area to volume ratio of the WC protrusion 66, the greater the Co
depletion will be, and the lower the average thermal expansion coefficient
for the protrusion 66. This will result in an improved match between the
WC substrate 60 and the PCD layer 50, thereby enhancing the performance
through improved residual stress at the WC-PCD interface 52.
The present invention is valuable as an improved way to manufacture PDC
cutters with unique properties. The WC-PCD interface geometry of the
present invention provides a better match between the WC substrate and the
PCD layer. The primary advantage of this interface geometry being enhanced
performance and less installation and/or brazing breakage due to improved
residual stress at the WC-PCD interface.
While the present invention has been described with reference to one or
more preferred embodiments, such embodiments are merely exemplary and are
not intended to be limiting or represent an exhaustive enumeration of all
aspects of the invention. The scope of the invention, therefore, shall be
defined solely by the following claims. Further, it will be apparent to
those of skill in the art that numerous changes may be made in such
details without departing from the spirit and the principles of the
invention.
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